Miniature snap acting thermostatic switch



Oct. 19, 1965 L. MARcoUx 3,213,250

MINIATURE SNAP ACTING THERMOSTATIC SWITCH Filed Nov. 30, 1962 2 Sheets-Sheet l fgf.

33 i VZ( @M44 Oct. 19, 1965 MARcoux 3,213,250

MINIATURE SNAP ACTING THERMOSTATIG SWITCH Filed Nov. 30. 1962 2 Sheets-Sheet 2 Zullen tor; Zea .Maranza/3 United States Patent O 3,213,250 MINIATURE SNAP ACTING THERMOSTATIC SWITCH Leo Marcoux, Pawtucket, RI., assigner to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Nov. 30, 1962, Ser. No. 241,238 6 Claims. (Cl. 2011-138) This invention relates to thermally responsive electrical switches and in particular to such switches which are especially suited for miniaturized, hermetically sealed constructions and methods for making the same.

Among the several objects of this invention may be noted the provision of new and improved thermally responsive electrical switches which permit fast response, and are adapted for miniaturization so as to be conveniently insertable into small spaces adjacent the heated parts to which a temperature response is to be made by the switch; the provision of such switches which are especially adapted for hermetically sealed constructions; the provision of such switches which are precise, accurate, compact and reliable in operation; the provision of such switches which provide for improved vibration and shock resistance and which are relatively insensitive to position orientation; the provision of such switches which embody a minimum number of parts, are relatively simple in construction and are economical to assemble and manufacture; and the provision of a relatively simple and inexpensive method for making such switches.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts, all of which will be exemplified in the structures and methods hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which several of the various possible embodiments of the invention are illustrated:

FIG. 1 is a top plan view of a thermally responsive electrical switch according to the present invention;

FIG. 2 is a sectional view taken on line 2 2 of FIG. 1 showing the parts in a contacts-closed position;

FIG. 3 is a fragmentary sectional view similar to FIG. 2 showing the parts in a contacts-open position;

FIG. 4 is a sectional view taken on line 4 4 of FIG. 2;

FIG. 5 is a top plan view of a spring member used in the switch shown in FIGS. 1 4;

FIG. 6 is an elevational view of the spring member shown in FIG. 5; and

FIG. 7 is an exploded elevational View of the switch shown in FIG. 2.

Similar reference characters indicate corresponding parts throughout the several views of the drawings. Dimensions of certain of the parts, as shown in the drawings, have been modified and/ or exaggerated for the purpose of clarity of illustration.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The switches of the present invention are of the type which employ a thermally responsive bimetallic snapacting disc for actuation of a pair of electrical contacts.

3,213,250 Patented Oct. 19, 1965 Considerable difficulty is experienced in the manufacture of miniaturized versions of switches of this type. Many problems of fabrication and calibration are encountered with the miniaturized constructions which either do not exist or are not as severe with the larger size switches of this type. Examples of such problems are: preventing actuation of the contacts by creep movement prior to the occurrence of snap action; mounting of the snap-acting member; hermetic sealing; and economical manufacture and assembly.

The present invention solves or at least minimizes these problems and provides a switch which affords additional advantages which will be described below.

Referring now to FIGS. 1-4, there is shown a rst embodiment of the invention, generally referred to by numeral 10, and which takes the form of a hermeticallysealed, thermally responsive, snap-acting, electrical switch.

Switch 10 includes a housing or casing provided by a pair of closure end plate members 12, 14 formed of a good electrically and thermally conductive material such as, for example, silver, brass or cold rolled steel, and an open ended cylindrical, tubular sleeve member 16 formed of electrically insulating material, for example, ceramic. Each of plate members 12 and 14 respectively include a circumferentially extending recessed shoulder portion 18 and 20 so that the plate members snugly seat on the sleeve 16 to close the open ends thereof, as best seen in FIGS. 2 and 3. A circumferentially extending metal layer 22 is bonded or deposited on the ends of sleeve 16 which abut plate members 12 and 14 to facilitate sealing of the switch 10 which will be more fully described below. Metal layer 22 is preferably of the type which is readily solderable such as, for example, a molybdenum-manganese alloy.

Disposed in supportive and electrically conductive er1- gagement with the interior surface of plate 14 is a spring member 24 formed of a spring material having good electrically and thermally conductive properties. A suitable example is beryllium copper. Spring member 24- is circular in form and has a diameter which closely approximates that of the interior diameter of sleeve 16. As best seen in FIGS. 5 and 6, spring 24 has a plurality of struckout spring fingers 26, 28 and 30 which are biased for movement to one side and out of the plane of the spring member 24.

Resting on or supported on spring ngers 26, 28 and 30 is a snap-acting composite thermostatic bimetallic disc-type element 32 of the type disclosed, for example, in United States Patent No. 1,448,240. Disc 32 is provided with a non-developable or deformed portion responsible for its snap action and has a diameter substantially equal to that of spring 26 and the inside diameter of sleeve 16. As best seen in FIG. 4, an electrical contact 34 is electrically connected and secured, as by welding, to the disc 32 at a central portion thereof for movement in response to snap movement of disc 32.

The interior surface of plate member 12 provides an electrical contact surface 36 for mating engagement with contact 34. Plates 12 and 14 may be coated or plated with a low electrical resistance precious metal, for example, a silver or gold alloy, to improve electrical conductivity. Plates 12 and 14 are preferably respectively provided with exteriorly extending cylindrical terminals 38 and 39 projecting substantially perpendicularly from the plate members. Electrical leads 41 and' 43 are respectively electrically connected to terminals 38 and 39. If desired, terminals 38 and 39 may be omitted and leads 41 and 43 can be attached directly to plates 12 and 14. If desired, an electrical contact may be secured to plate 12 instead or relying on the contact surface 36.

Switch 10 also includes an annular, washer-like abutment member 40 formed of electrically insulating material, a suitable example of which is ceramic. Abutment 40 is telescopically disposed in sleeve 16 between disc 32 and plate 12, as best seen in FIGS. 2 and 3. The outer diameter of abutment itl closely approximates the interior diameter of sleeve 16 for a relatively snug sliding fit therebetween. Abutment 40 is urged for sliding movement toward engagement with plate 12 by spring 24 when disc 32 has snapped to the contacts-open FIG. 3 Condition.

Conventional means for preventing undesirable contact actuation by creep action prior to the occurrence of snap action (of the thermally responsive contact actuator) as employed in larger snap-acting thermally responsive devices are generally not practical or useful with miniaturized constructions of this type. According to the present invention, the thickness of abutment 40 is such that disc 32 will not he restricted against movement through engagement with abutment 4t) and plate 12 when disc 32 creeps from the contacts-closed toward the contacts-open position which, along with the cooperation between disc 32 and spring 24, serves to prevent or inhibit the disc from opening contacts 34 and 36 by creep action prior to the occurrence of snap action and renders switch especially suitable for miniaturized constructions. Switches according to the present invention have been made as small as 0.214 inch in diameter and 0.08() inch in height (excluding the height of terminals 38 and 39). The small size and low thermal mass advantageously affords fast thermal response by switch 10.

As best seen in FIG. 7, assembly of switch 1li can be accomplished by the following simple steps: dispose spring 24 on plate 14 and within sleeve 16; insert disc 32 in sleeve 16 so that it rests on the spring lingers 26, 28 and 30 and contact 34 faces upwardly as seen in FIG. 7; telescopically dispose abutment Washer 40 within sleeve 16; seat the plates 12 and 14 in the ends of sleeve 16, which compresses spring lingers 26, 23 and 30; apply a clamping or holding pressure axially against terminals 38 and 39 as suggested by the arrows in FIG. 7, to hold the parts together in assembled relation; flux the assembly while under pressure and thereafter completely immerse the assembly while under pressure into a molten solder to bond and secure the plates 12 and 14 to sleeve 16 and to hermetically seal switch 10. The dip solder step results in the formation of two circumferentially extending fillets 44 and 46 (see FIGS. 2 and 3). The solder adheres or bonds only to the exposed metal surfaces, e.g., that of plates 12, 14 and layer 22 but does not adhere to the electrically insulating exposed surface portions of sleeve 16. If desired, hermetically sealed switch 1@ can further be encapsulated (not shown) as by dipping in an electrically insulating material such as a thermo-setting resinous or epoxy material. The shoulders 18 which snugly seat on sleeve 16 conveniently prevent the entry of solder into the interior of switch 10 during the dipping and hermetic sealing operation. The

solder dip assembly method of this invention is particularly suited for automated mass production techniques.

FIG. 2 shows switch 10 in the final assembled and hermetically sealed condition. Switch 10 provides an electrically conductive current path leading from terminal 38, through plate 12, to contact surface 36, to contact 34, through thermostatic disc 32, to electrically conductive spring member 24, to the electrically conductive plate 14, to terminal 39.

It will be understood that a snap-acting thermostatic disc, such as herein contemplated, is one which snaps abruptly form one dished condition to an oppositely dished condition. Abrupt snapping occurs at least in part because of temperature induced stresses set up in the disc, which upon change (e.g., increase) of temperature ultimately effects a very rapid and violent reversal of curvature of the disc. The peripheral portion of the disc tends to restrain the remainder of the disc from simply flattening out or fiexing until the temperature induced stresses become so high that the disc abruptly and violently snaps through the hoop-like peripheral portion. The amount of restraint to snapping presented by the peripheral portion of the disc will be influenced by the magnitude of forces exerted against the peripheral portion of the disc by the disc mounting or supporting means and also by the point of application of these forces to the disc. It will be clear that variation in the forces applied to the peripheral portion and in the point of application to the peripheral portion of the disc can affect the operating characteristics of the disc.

Annularly extending abutment washer 4f) overlies and is disposed adjacent the peripheral portion of disc 32 and is adapted for engagement therewith. Disc 32 also bears against abutment 4t) in snapping from the contacts-closed position shown in FIG. 2 to the contactsopen position shown in FIG. 3. Spring lingers 26, 28 and 30 engage one side of disc 32 at a peripheral portion thereof and at all times urge the peripheral portion of disc 32 for movement upwardly (as seen in FIG. 2) toward engagement with stop or abutment fit). Upward movement of washer itl is limited by its engagement with plate 12. Spring 24 by engaging the peripheral portion of the disc 32 does not significantly interfere with the snap acting characteristics and temperature of operation of the disc. Spring 24 is preferably of the type having a low spring rate. An example of a suitable spring rate is on the order of 5 to l5 lbs. per inch. The low spring rate is preferred so as to further minimize the influence of the spring 24 on the snap-acting characteristics and operation of the disc 32 and to permit greater tolerance in spacing between the abutment 40 (when the latter engages plate 12) and the interior surface of plate 14 and in the thickness of abutment 40, which eliminates the need for expensive gauged selective assembly of parts. The three point engagement between the spring 24- and disc 32 equalizes the spring load or force applied against the disc so as to further minimize interference of the spring with the snap-acting operation of the disc 32. When disc 32 is in the FIG. 2 contactsclosed position, washer dfi is not urged toward engagement with plate 12 and may rest on disc 32. Washer 40, however, is relatively light weight and does not significantly intiuence the snap-acting operation of disc 32.

rlhe fact that a number of the elements of switch 10 serve multiple functions, contributes significantly toward providing a simple, minimum number of parts construction which is especially suited for miniaturization and which can be quickly and easily assembled by the method described above. For example, abutment 4@ co-operates with spring member 24 which constantly urges disc 32 for movement toward engagement with abutment 46, to maintain the contacts 34 and 36 in a contacts-open or separated condition after the disc has snapped to the FIG. 3 (contacts-open) condition. This co-operation between spring 24, disc 32 and stop fit) additionally provides for improved and increased vibration and shock resistance of the switch 10; assures a maximum or at least a substantial contactsopening gap when the disc is in the FIG. 3 condition; serves to maintain desired contact pressure between contacts 34 and 36 in the FIG. 2 contacts-closed condition; provides a good electrical connection between the disc 32 and the electrically conductive end plate 14; provides a good heat transfer connection between plate 14 and disc 32 to afford a fast thermal response; and renders switch 10 relatively insensitive to position orientation.

The present invention avoids the necessity for fixedly securing the disc 32 to any mounting means or supporting means, a factor which is particularly significant in a miniaturized construction, while providing a convenient means for preventing creep opening of the contacts prior to snap action. While a specific form of spring member 24 has been described and shown, it will be understood that other forms of electrically conductive spring members may also be used for engaging the peripheral portion of the disc to urge the latter toward engagement with the stop or abutment 40. If desired, abutment washer 40 could be formed integrally with or xedly secured to plate 12 or sleeve 16. However, the depth or height of abutment 40 would still have to be selected so that the distance between the disc 32, engaging surface of abutment 40 and interior surface of plate 14 is such as to provide the multiple functions described above for the co-operation between spring 24, disc 32 and stop 40.

In view of the above, it will be seen that the several objects of the invention are achieved, and other advantageous results attained.

As many changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above descripion or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope ofthe invention.

I claim:

il. A thermally responsive electrical switch comprising an open ended tubular sleeve formed of electrically insulating material; tirst and second plate members each secured to and closing a respective end of said sleeve and each having an electrically conductive portion; a composite thermally responsive snap-acting element disposed within said sleeve, said element having a deformed portion responsible for its snap action; electrically conductive spring means disposed in said housing interposed between and in electrically conductive contact with said electrically con ductive portion of said first plate member and element, thereby establishing an electrically conductive path therebetween; a movable electrically conductive contact carried on said thermally responsive element in electrically conductive relationship therewith and mounted for movement in response to snap movement of said element into and out of electrically conductive relationship with the electrically conductive portion of said second plate member; an annular abutment member positioned in said sleeve intermediate said element and second plate member for engagement with a portion of said element; and said spring means urging said element for movement in a direction away from said electrically conductive portion of said first plate member and toward engagement with said abutment member.

2. A hermetically sealed thermally responsive electrical switch adapted for miniaturization comprising an open ended tubular sleeve formed of electrically insulating material; rst and second thermally and electrically conductive plate members each bonded to and closing a respective end of said sleeve to provide a hermetically sealed switch housing; a composite thermally responsive snapacting element disposed within said sleeve, said element having a deformed portion responsible for its snap action; electrically conductive spring means disposed in said housing interposed between and in electrically conductive contact with said tirst plate member and element, thereby establishing an electrically conductive path therebetween; said spring means engaging said element adjacent the outer periphery thereof; a movable electrically conductive contact carried by and electrically connected to a central portion of said thermally responsive element and mounted for movement in response to snap movement of said element into and out of electrically conductive relationship with said second plate member; an annular abutment member positioned in `said sleeve intermediate said element and second plate member for engagement with a peripheral portion of said element; and said spring means urging said element for movement in a direction away from said tirst plate member and toward engagement with said abutment member.

3. The switch as set forth in claim 2 and wherein said spring means comprises a metal spring member formed of thermally and electrically conductive material and having a plurality of spring fingers engaging said element at spaced portions adjacent the outer periphery of said element.

4. A hermetically sealed thermally responsive electrical switch adapted for miniaturization comprising an open ended tubular sleeve formed of electrically insulating material; tirst and second thermally and electrically conductive plate members each abutting and secured, as by soldering, to a respective end of said sleeve to provide a hermetically sealed switch housing; the ends of said sleeve which abut said plate members being provided with a coating of solderable material to facilitate hermetic sealing; a composite thermally responsive snap-acting element disposed within said sleeve, said element having a deformed portion responsible for its snap action; electrically conductive spring means disposed in said housing interposed between and in electrically conductive contact with said first plate member and element, thereby establishing an electrically conductive path therebetween; said spring means engaging said element adjacent the outer periphery thereof; a movable electrically conductive contact carried by and electrically connected to a central portion of said thermally responsive element and mounted for movement in response to snap movement of said element into and out of electrically conductive relationship with said second plate member; an annular abutment member formed of electrically insulating material positioned in said sleeve intermediate said element and said second plate member for engagement with a peripheral portion of said element; and said spring means urging said element for movement in a direction away from said first plate member and toward engagement with said abutment member.

5. The switch as set forth in claim 4 and wherein said abutment member is washer-like in form and formed of a ceramic; said abutment member being telescopically disposed within `said sleeve and being movable relative to said element and said second plate member wherein said spring means comprises a metal spring member formed of thermally and electrically conductive material and having a plurality of spring lingers engaging said element at spaced portions adjacent the outer periphery of said element.

6. The switch as set forth in claim 4 and wherein each of said iirst and second plate members are formed of metal and are provided with peripherally extending shoulder portions which mate and closely intertit with the open ends of said sleeve and wherein said sleeve is formed of a ceramic material and wherein said electrically conductive portion of said second plate member comprises a surface of said second plate member.

References Cited by the Examiner UNITED STATES PATENTS 2,508,510 5/50 Gillespie 20G-138 2,811,611 10/57 Odenwald 200-138 2,839,635 6/58 Hasselhorn 200-118 2,934,628 4/60 Massar et al. 200-142 OTHER REFERENCES German application No. 1,021,920, printed Jan. 1, 1958.

BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEFER, Examiner. 

1. A THERMALLY RESPONSIVE ELECTRICAL SWITCH COMPRISING AN OPEN ENDED TUBULAR SLEEVE FORMED OF ELECTRICALLY INSULATING MATERIAL; FIRST AND SECOND PLATE MEMBERS EACH SECURED TO AND CLOSING A RESPECTIVE END OF SAID SLEEVE AND EACH HAVING AN ELECTRICALLY CONDUCTIVE PORTION; A COMPOSITE THERMALLY RESPONSIVE SNAP-ACTING ELEMENT DISPOSED WITHIN SAID SLEEVE, AND ELEMENT HAVING A DEFORMED PORTION RESPONSIBLE FOR ITS SNAP ACTION; ELECTRICALLY CONDUCTIVE SPRING MEANS DISPOSED IN SAID HOUSING INTERPOSED BETWEEN AND IN ELECTRICALLY CONDUCTIVE CONTACT WITH SAID ELECTRICALLY CONDUCTIVE PORTION OF SAID FIRST PLATE MEMBER AND ELEMENT, THEREBY ESTABLISHING AN ELECTRICALLY CONDUCTIVE PATH THEREBETWEEN; A MOVABLE ELECTRICALLY CONDUCTIVE CONTACT CARRIED ON SAID THERMALLY RESPONSIVE ELEMENT IN ELECTRICALLY CONDUCTIVE RELATIONSHIP THEREWITH AND MOUNTED FOR MOVEMENT IN RESPONSE TO SNAP MOVEMENT OF SAID ELEMENT INTO AND OUT OF ELECTRICALLY CONDUCTIVE RELATIONSHIP WITH THE ELECTRICALLY CONDUCTIVE PORTION OF SAID SECOND PLATE MEMBER; AN ANNULAR ABUTMENT MEMBER POSITIONED IN SAID SLEEVE INTERMEDIATE SAID ELEMENT AND SECOND PLATE MEMBER FOR ENGAGEMENT WITH A PORTION OF SAID ELEMENT; AND SAID SPRING MEANS URGING SAID ELEMENT FOR MOVEMENT IN A DIRECTION AWAY FROM SAID ELECTRICALLY CONDUCTIVE PORTION OF SAID FIRST PLATE MEMBER AND TOWARD ENGAGEMENT WITH SAID ABUTMENT MEMBER. 